Unveiling the role of tumor reactive stroma in cholangiocarcinoma: an opportunity for new therapeutic strategies.

Cholangiocarcinoma (CCA) is a very aggressive neoplasm, whose incidence has steadily increased in the last decade. Despite its growing epidemiological impact, therapeutic chances with a curative intent are still limited to surgical resection and, in highly selected cases, to liver transplantation. Unfortunately, in most cases at the time of diagnosis, CCA has already metastasized to regional lymph nodes, thereby reducing the opportunities for curative treatment. Mechanisms governing CCA invasiveness are unclear. A critical element of CCA is the abundant "tumor reactive stroma", which develops in close association with tumor growth. An abundant reactive stroma is present in a number of carcinomas characterized by strong invasiveness, namely gastric, colorectal and pancreatic cancers, as well as breast cancer. In tumor stroma, a variety of signals and mediators are reciprocally exchanged between stromal and cancer cells that, in turn acquire pro-invasive properties. These paracrine communications have started to be elucidated only recently, and may represent targets amenable of specific therapeutic intervention. In this review, we will highlight the cell types that compose the tumor reactive stroma in CCA and some of the molecular interactions possibly responsible for increased invasiveness of CCA. The possibility of dissecting, and likely exploiting, these interactions for potential new treatments will be also described.